Novel Bioactive Titanate Layers Formed on Ti Metal and Its Alloys by Chemical Treatments

Enhancement of in vitro antibacterial activity and bioactivity of iodine-loaded titanium by micro-scale regulation using mixed-acid treatment

Postoperative infection and subsequent device loss are serious complications in the use of titanium dental implants and plates for jawbone reconstruction. We have previously reported that NaOH-CaCl2 -thermal-ICl3 -treated titanium (NaCaThIo) has a nano-scale surface and exhibits antibacterial activity against Staphylococcus aureus. The present study examined the surface properties of mixed-acid treated and then iodine-treated titanium (MA-NaCaThIo), and evaluated oral antibacterial activity and cytotoxicity compared with the results obtained with NaCaThIo. MA-NaCaThIo formed a surface layer with a nano-scale network structure having microscale irregularities, and both the thickness of the surface layer (1.49 ± 0.16 μm) and the average surface roughness (0.35 ± 0.03 μm) were significantly higher than those of NaCaThIo. Furthermore, MA-NaCaThIo maintained high hydrophilicity with a contact angle of 7.5 ± 1.7° even after 4 weeks, as well as improved apatite formation, iodine ion release, and antibacterial activity against Prevotella intermedia compared to NaCaThIo. Cell culture test revealed that MA-NaCaThIo exhibited no cytotoxicity against MG-63 and Vero cells, while increased cell proliferation, ALP activity and mineralization of MG-63 compared to NaCaThIo. This treated titanium is expected to be useful for the development of next-generation titanium devices having both bone-bonding and antibacterial properties.

Titanium modification using bioactive titanate layer with divalent ions and coordinated ciprofloxacin - Assessment of drug distribution using FT-IR imaging

The paper presents a new method of titanium alloy (Ti6Al4V) modification using bioactive titanate layers containing various divalent ions (Ca2+, Mg2+, Sr2+, Zn2+) and surface-coordinated ciprofloxacin. Due to the coordination of ciprofloxacin (antibiotic) on the surface of the alloy, it has great application potential. In the paper, the influence of a given cation on the effectiveness of drug sorption was determined. The most effective cation was zinc and the least effective was calcium. The distribution of the antibiotic on the alloy surface was determined using FT-IR imaging. The antibiotic was evenly distributed on alloys modified with magnesium, strontium and zinc titanates. In the case of calcium titanate, the analysis could not be performed because the amount of the drug was too small. The release profiles of ciprofloxacin indicate that it can be released for as long as 3 h for strontium and zinc titanates. The biocompatibility of the obtained materials is indicated by the results of the BSA adsorption, and HA growth test. The obtained results confirm that the proposed modification can be used in the modification of titanium implants. The big advantage of this layer is that ciprofloxacin is coordinated on the surface of the material and thus will not be removed during the surgical procedure. The creation of this type of layer may in the future allow for fewer perioperative infections, and thus fewer complications.

Hypersensitivity reactions to metals in spine surgery

Hypersensitivity to orthopedic devices is a rare condition with an underestimated incidence due to the lack of diagnostic guideline and ambiguous clinical manifestations. Although hypersensitivity to metal is common, a few cases of hypersensitivity reactions have been reported after spinal instrumentation. Spinal fusion and stabilization require a wide range of devices such as screws, wires, bands, and artificial disk replacement devices. Spinal instrumented surgeries are different from total joint arthroplasty in several aspects such as degree and pattern of motion, loading environment, and adjacent tissues with distinct characteristics. The interval for hypersensitivity reactions to occur after spinal metallic implantation is usually weeks to months. The present review covers the topic of hypersensitivity reactions that have been reported after spinal surgeries with the focus on cutaneous presentations.

TiO2/HA and Titanate/HA Double-Layer Coatings on Ti6Al4V Surface and Their Influence on In Vitro Cell Growth and Osteogenic Potential

Hydroxyapatite (HA) layers are appropriate biomaterials for use in the modification of the surface of implants produced inter alia from a Ti6Al4V alloy. The issue that must be solved is to provide implants with appropriate biointegration properties, enabling the permanent link between them and bone tissues, which is not so easy with the HA layer. Our proposition is the use of the intermediate layer ((IL) = TiO₂, and titanate layers) to successfully link the HA coating to a metal substrate (Ti6Al4V). The morphology, structure, and chemical composition of Ti6Al4V/IL/HA systems were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDS). We evaluated the apatite-forming ability on the surface of the layer in simulated body fluid. We investigated the effects of the obtained systems on the viability and growth of human MG-63 osteoblast-like cells, mouse L929 fibroblasts, and adipose-derived human mesenchymal stem cells (ADSCs) in vitro, as well as on their osteogenic properties. Based on the obtained results, we can conclude that both investigated systems reflect the physiological environment of bone tissue and create a biocompatible surface supporting cell growth. However, the nanoporous TiO₂ intermediate layer with osteogenesis-supportive activity seems most promising for the practical application of Ti6Al4V/TiO₂/HA as a system of bone tissue regeneration.

Drug distribution evaluation using FT-IR imaging on the surface of a titanium alloy coated with zinc titanate with potential application in the release of drugs for osteoporosis

The drugs most commonly used in the treatment of osteoporosis are bisphosphonates. This disease results in low mineral density and a weakened bone microstructure. The delivery methods for these drugs have many disadvantages, and new ones are being searched for. In this work, biocompatible zinc titanate coated titanium implants were obtained as potential new carriers for drugs. Such a material will release the drug, and it will have antibacterial properties. Gradual release of the bisphosphonate will have a positive effect on the recovery process and osteointegration. In addition, the drug will be released around the affected bones. The effectiveness of the modification and attachment of the drug was confirmed by SEM, XPS, EDS, FT-IR imaging, and UV-VIS. It was shown that the risedronate could be almost completely released upon contact with body fluids within a week. The drug is evenly distributed over the entire surface of the alloy as confirmed by FT-IR imaging. The results presented in this work will allow for the preparation of endoprostheses that release the drug and have antibacterial properties.

A Novel Nanostructured Surface on Titanium Implants Increases Osseointegration in a Sheep Model

BACKGROUND

A nanostructured titanium surface that promotes antimicrobial activity and osseointegration would provide the opportunity to create medical implants that can prevent orthopaedic infection and improve bone integration. Although nanostructured surfaces can exhibit antimicrobial activity, it is not known whether these surfaces are safe and conducive to osseointegration.

QUESTIONS/PURPOSES

Using a sheep animal model, we sought to determine whether the bony integration of medical-grade, titanium, porous-coated implants with a unique nanostructured surface modification (alkaline heat treatment [AHT]) previously shown to kill bacteria was better than that for a clinically accepted control surface of porous-coated titanium covered with hydroxyapatite (PCHA) after 12 weeks in vivo. The null hypothesis was that there would be no difference between implants with respect to the primary outcomes: interfacial shear strength and percent intersection surface (the percentage of implant surface with bone contact, as defined by a micro-CT protocol), and the secondary outcomes: stiffness, peak load, energy to failure, and micro-CT (bone volume/total volume [BV/TV], trabecular thickness [Tb.Th], and trabecular number [Tb.N]) and histomorphometric (bone-implant contact [BIC]) parameters.

METHODS

Implants of each material (alkaline heat-treated and hydroxyapatite-coated titanium) were surgically inserted into femoral and tibial metaphyseal cancellous bone (16 per implant type; interference fit) and in tibial cortices at three diaphyseal locations (24 per implant type; line-to-line fit) in eight skeletally mature sheep. At 12 weeks postoperatively, bones were excised to assess osseointegration of AHT and PCHA implants via biomechanical push-through tests, micro-CT, and histomorphometry. Bone composition and remodeling patterns in adult sheep are similar to that of humans, and this model enables comparison of implants with ex vivo outcomes that are not permissible with humans. Comparisons of primary and secondary outcomes were undertaken with linear mixed-effects models that were developed for the cortical and cancellous groups separately and that included a random effect of animals, covariates to adjust for preoperative bodyweight, and implant location (left/right limb, femoral/tibial cancellous, cortical diaphyseal region, and medial/lateral cortex) as appropriate. Significance was set at an alpha of 0.05.

RESULTS

The estimated marginal mean interfacial shear strength for cancellous bone, adjusted for covariates, was 1.6 MPa greater for AHT implants (9.3 MPa) than for PCHA implants (7.7 MPa) (95% CI 0.5 to 2.8; p = 0.006). Similarly, the estimated marginal mean interfacial shear strength for cortical bone, adjusted for covariates, was 6.6 MPa greater for AHT implants (25.5 MPa) than for PCHA implants (18.9 MPa) (95% CI 5.0 to 8.1; p < 0.001). No difference in the implant-bone percent intersection surface was detected for cancellous sites (cancellous AHT 55.1% and PCHA 58.7%; adjusted difference of estimated marginal mean -3.6% [95% CI -8.1% to 0.9%]; p = 0.11). In cortical bone, the estimated marginal mean percent intersection surface at the medial site, adjusted for covariates, was 11.8% higher for AHT implants (58.1%) than for PCHA (46.2% [95% CI 7.1% to 16.6%]; p < 0.001) and was not different at the lateral site (AHT 75.8% and PCHA 74.9%; adjusted difference of estimated marginal mean 0.9% [95% CI -3.8% to 5.7%]; p = 0.70).

CONCLUSION

These data suggest there is stronger integration of bone on the AHT surface than on the PCHA surface at 12 weeks postimplantation in this sheep model.

CLINICAL RELEVANCE

Given that the AHT implants formed a more robust interface with cortical and cancellous bone than the PCHA implants, a clinical noninferiority study using hip stems with identical geometries can now be performed to compare the same surfaces used in this study. The results of this preclinical study provide an ethical baseline to proceed with such a clinical study given the potential of the alkaline heat-treated surface to reduce periprosthetic joint infection and enhance implant osseointegration.

Zeolitic Imidazolate Framework‑8 (ZIF-8) modified titanium alloy for controlled release of drugs for osteoporosis

The aim of this work was to prepare a biocompatible implant material that enables the release of drug for osteoporosis—risedronate. To achieve this goal, a titanium implant coated with a biocompatible Zeolitic Imidazolate Framework 8 (ZIF-8) layer was prepared that promotes osseointegration at the bone-implant interface. The modifications of the titanium alloy as well as sorption and desorption processes were confirmed using a variety of methods: SEM, EDS XPS, and FT-IR imaging (to determine surface modification, drug distribution, and risedronate sorption), and UV–Vis spectroscopy (to determine drug sorption and release profile). Both the ZIF-8 layer and the drug are evenly distributed on the surface of the titanium alloy. The obtained ZIF-8 layer did not contain impurities and zinc ions were strongly bounded by ZIF-8 layer. The ZIF-8 layer was stable during drug sorption. The drug was released in small doses for 16 h, which may help patients recover immediately after surgery. This is the first case of using ZIF-8 on the surface of the titanium alloy as carrier that releases the drug under the influence of body fluids directly at the site of the disease. It is an ideal material for implants designed for people suffering from osteoporosis.

On-Growth and In-Growth Osseointegration Enhancement in PM Porous Ti-Scaffolds by Two Different Bioactivation Strategies: Alkali Thermochemical Treatment and RGD Peptide Coating

A lack of primary stability and osteointegration in metallic implants may result in implant loosening and failure. Adding porosity to metallic implants reduces the stress shielding effect and improves implant performance, allowing the surrounding bone tissue to grow into the scaffold. However, a bioactive surface is needed to stimulate implant osteointegration and improve mechanical stability. In this study, porous titanium implants were produced via powder sintering to create different porous diameters and open interconnectivity. Two strategies were used to generate a bioactive surface on the metallic foams: (1) an inorganic alkali thermochemical treatment, (2) grafting a cell adhesive tripeptide (RGD). RGD peptides exhibit an affinity for integrins expressed by osteoblasts, and have been reported to improve osteoblast adhesion, whereas the thermochemical treatment is known to improve titanium implant osseointegration upon implantation. Bioactivated scaffolds and control samples were implanted into the tibiae of rabbits to analyze the effect of these two strategies in vivo regarding bone tissue regeneration through interconnected porosity. Histomorphometric evaluation was performed at 4 and 12 weeks after implantation. Bone-to-implant contact (BIC) and bone in-growth and on-growth were evaluated in different regions of interest (ROIs) inside and outside the implant. The results of this study show that after a long-term postoperative period, the RGD-coated samples presented higher quantification values of quantified newly formed bone tissue in the implant's outer area. However, the total analyzed bone in-growth was observed to be slightly greater in the scaffolds treated with alkali thermochemical treatment. These results suggest that both strategies contribute to enhancing porous metallic implant stability and osteointegration, and a combination of both strategies might be worth pursuing.

A micro/nano-biomimetic coating on titanium orchestrates osteo/angio-genesis and osteoimmunomodulation for advanced osseointegration

Osseointegration is a sophisticated bone and implant healing process comprising of initial hematoma formation, immediate osteoimmunomodulation, angiogenesis, and osteogenesis. To fulfill rapid and satisfying osseointegration, this study developed a biomimetic implant coating that could confer the intraosseous implants a systematical regulation of the participatory processes. Herein, we shaped dissimilar nano-scale (NS) to form highly biomimetic structures of natural extracellular matrix (ECM) of the host bone and bone healing hematoma with micro/nano-scale (MNS) titania fiber-like network on the surface of titanium (Ti) implants. In vitro experiments revealed that the MNS not only facilitated osteogenic and angiogenic differentiation of bone marrow stromal cells (BMSCs) and endothelial cells, respectively, but also suppressed M1 macrophages (MΦs), whereas, stimulated pro-healing M2 phenotype. Notably, BMSCs on MNS surfaces enabled a significant immunomodulatory effect on MΦs resulting in the downregulation of inflammation-related cell signaling pathways. The favorable osteoimmune microenvironment manipulated by MNS further facilitated osteo-/angio-genesis via the crosstalk of multi-signaling pathways. In vivo evaluation mirrored the aforementioned results, and depicted that MNS induced ameliorative osseointegration when compared with the NS as well as the pristine Ti implant. The study demonstrated the modulatory effect of the multifaceted biomimetic structure on spatiotemporal regulation of the participatory processes during osseointegration.

Iodine-Loaded Calcium Titanate for Bone Repair with Sustainable Antibacterial Activity Prepared by Solution and Heat Treatment

In the orthopedic and dental fields, simultaneously conferring titanium (Ti) and its alloy implants with antibacterial and bone-bonding capabilities is an outstanding challenge. In the present study, we developed a novel combined solution and heat treatment that controllably incorporates 0.7% to 10.5% of iodine into Ti and its alloys by ion exchange with calcium ions in a bioactive calcium titanate. The treated metals formed iodine-containing calcium-deficient calcium titanate with abundant Ti-OH groups on their surfaces. High-resolution XPS analysis revealed that the incorporated iodine ions were mainly positively charged. The surface treatment also induced a shift in the isoelectric point toward a higher pH, which indicated a prevalence of basic surface functionalities. The Ti loaded with 8.6% iodine slowly released 5.6 ppm of iodine over 90 days and exhibited strong antibacterial activity (reduction rate >99%) against methicillin-resistant Staphylococcus aureus (MRSA), S. aureus, Escherichia coli, and S. epidermidis. A long-term stability test of the antibacterial activity on MRSA showed that the treated Ti maintained a >99% reduction until 3 months, and then it gradually decreased after 6 months (to a 97.3% reduction). There was no cytotoxicity in MC3T3-E1 or L929 cells, whereas apatite formed on the treated metal in a simulated body fluid within 3 days. It is expected that the iodine-carrying Ti and its alloys will be particularly useful for orthopedic and dental implants since they reliably bond to bone and prevent infection owing to their apatite formation, cytocompatibility, and sustainable antibacterial activity.

Controlled release of the drug for osteoporosis from the surface of titanium implants coated with calcium titanate

The most popular drugs used to prevent osteoporosis that causes low mineral density and weakened microstructure of bones are bisphosphonates. Bisphosphonates can be administered in several ways, but each delivery method has drawbacks. Due to this, new methods of their delivery are being sought. Titanium implants coated with calcium titanate were prepared in this work as carriers for bisphosphonates. Such a modification has been proposed in order to improve the therapeutic properties of the implant. Slow release of the drug at a constant level will positively affect the recovery process and osteointegration. Furthermore, the drug will be slowly released very close to the area affected by osteoporosis. These studies were confirmed, using a variety of methods: EDS and XPS (to examine surface modification and drug sorption), Raman mapping (to proof the presence of the drug on the entire surface of the material) and UV-VIS spectroscopy (to determine bisphosphonate sorption and release profile). It was proved that the active substance (sorbed on the implant) could be completely released upon contact with body fluids within a month. The obtained results will allow for the production of endoprostheses dedicated to patients with osteoporosis in the future.

The moonlighting activities of dihydrolipoamide dehydrogenase: Biotechnological and biomedical applications

Dihydrolipoamide dehydrogenase (DLDH) is a homodimeric flavin-dependent enzyme that catalyzes the NAD⁺ -dependent oxidation of dihydrolipoamide. The enzyme is part of several multi-enzyme complexes such as the Pyruvate Dehydrogenase system that transforms pyruvate into acetyl-co-A. Concomitantly with its redox activity, DLDH produces Reactive Oxygen Species (ROS), which are involved in cellular apoptotic processes. DLDH possesses several moonlighting functions. One of these is the capacity to adhere to metal-oxides surfaces. This was first exemplified by the presence of an exocellular form of the enzyme on the cell-wall surface of Rhodococcus ruber. This capability was evolutionarily conserved and identified in the human, mitochondrial, DLDH. The enzyme was modified with Arg-Gly-Asp (RGD) groups, which enabled its interaction with integrin-rich cancer cells followed by "integrin-assisted-endocytosis." This allowed harnessing the enzyme for cancer therapy. Combining the TiO₂ -binding property with DLDH's ROS-production, enabled us to develop several medical applications including improving oesseointegration of TiO₂ -based implants and photodynamic treatment for melanoma. The TiO₂ -binding sites of both the bacterial and human DLDH's were identified on the proteins' molecules at regions that overlap with the binding site of E3-binding protein (E3BP). This protein is essential in forming the multiunit structure of PDC. Another moonlighting activity of DLDH, which is described in this Review, is its DNA-binding capacity that may affect DNA chelation and shredding leading to apoptotic processes in living cells. The typical ROS-generation by DLDH, which occurs in association with its enzymatic activity and its implications in cancer and apoptotic cell death are also discussed.

Assessment of Titanate Nanolayers in Terms of Their Physicochemical and Biological Properties

The surface modification of titanium substrates and its alloys in order to improve their osseointegration properties is one of widely studied issues related to the design and production of modern orthopedic and dental implants. In this paper, we discuss the results concerning Ti6Al4V substrate surface modification by (a) alkaline treatment with a 7 M NaOH solution, and (b) production of a porous coating (anodic oxidation with the use of potential U = 5 V) and then treating its surface in the abovementioned alkaline solution. We compared the apatite-forming ability of unmodified and surface-modified titanium alloy in simulated body fluid (SBF) for 1–4 weeks. Analysis of the X-ray diffraction patterns of synthesized coatings allowed their structure characterization before and after immersing in SBF. The obtained nanolayers were studied using Raman spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy (DRIFT), and scanning electron microscopy (SEM) images. Elemental analysis was carried out using X-ray energy dispersion spectroscopy (SEM EDX). Wettability and biointegration activity (on the basis of the degree of integration of MG-63 osteoblast-like cells, L929 fibroblasts, and adipose-derived mesenchymal stem cells cultured in vitro on the sample surface) were also evaluated. The obtained results proved that the surfaces of Ti6Al4V and Ti6Al4V covered by TiO₂ nanoporous coatings, which were modified by titanate layers, promote apatite formation in the environment of body fluids and possess optimal biointegration properties for fibroblasts and osteoblasts.

The Use of Simulated Body Fluid (SBF) for Assessing Materials Bioactivity in the Context of Tissue Engineering: Review and Challenges

Some special implantable materials are defined as “bioactive” if they can bond to living bone, forming a tight and chemically-stable interface. This property, which is inherent to some glass compositions, or can be induced by applying appropriate surface treatments on otherwise bio-inert metals, can be evaluated in vitro by immersion studies in simulated body fluid (SBF), mimicking the composition of human plasma. As a result, apatite coating may form on the material surface, and the presence of this bone-like “biomimetic skin” is considered predictive of bone-bonding ability in vivo. This review article summarizes the story and evolution of in vitro bioactivity testing methods using SBF, highlighting the influence of testing parameters (e.g., formulation and circulation of the solution) and material-related parameters (e.g., composition, geometry, texture). Suggestions for future methodological refinements are also provided at the end of the paper.

Three-Dimensional Printed Porous Titanium Screw with Bioactive Surface Modification for Bone-Tendon Healing: A Rabbit Animal Model

The interference screw fixation method is used to secure a graft in the tibial tunnel during anterior cruciate ligament reconstruction surgery. However, several complications have been reported, such as biodegradable screw breakage, inflammatory or foreign body reaction, tunnel enlargement, and delayed graft healing. Using additive manufacturing (AM) technology, we developed a titanium alloy (Ti₆Al₄V) interference screw with chemically calcium phosphate surface modification technology to improve bone integration in the tibial tunnel. After chemical and heat treatment, the titanium screw formed a dense apatite layer on the metal surface in simulated body fluid. Twenty-seven New Zealand white rabbits were randomly divided into control and additive manufactured (AMD) screw groups. The long digital extensor tendon was detached and translated into a tibial plateau tunnel (diameter: 2.0 mm) and transfixed with an interference screw while the paw was in dorsiflexion. Biomechanical analyses, histological analyses, and an imaging study were performed at 1, 3, and 6 months. The biomechanical test showed that the ultimate pull-out load failure was significantly higher in the AMD screw group in all tested periods. Micro-computed tomography analyses revealed early woven bone formation in the AMD screw group at 1 and 3 months. In conclusion, AMD screws with bioactive surface modification improved bone ingrowth and enhanced biomechanical performance in a rabbit model.

Developing highly nanoporous titanate structures via wet chemical conversion of DC magnetron sputtered titanium thin films

Titanate structures have been widely investigated as biomedical component surfaces due to their bioactive, osteoinductive and antibacterial properties. However, these surfaces are limited to Ti and its alloys, due to the nature of the chemical conversion employed. The authors present a new method for generating nanoporous titanate structures on alternative biomaterial surfaces, such as other metals/alloys, ceramics and polymers, to produce bioactive and/or antibacterial properties in a simple yet effective way. Wet chemical (NaOH; 5 M; 60 °C; 24 h) conversion of DC magnetron sputtered Ti surfaces on 316L stainless steel were investigated to explore effects of microstructure on sodium titanate conversion. It was found that the more equiaxed thin films (B/300) generated the thickest titanate structures (ca. 1.6 μm), which disagreed with the proposed hypothesis of columnar structures allowing greater NaOH ingress. All film parameters tested ultimately generated titanate structures, as confirmed via EDX, SEM, XPS, XRD, FTIR and Raman analyses. Additionally, the more columnar structures (NB/NH & B/NH) had a greater quantity of Na (ca. 26 at.%) in the top portion of the films, as confirmed via XPS, however, on average the Na content was consistent across the films (ca. 5-9 at.%). Film adhesion for the more columnar structures (ca. 42 MPa), even on polished substrates, were close to that of the FDA requirement for plasma-sprayed HA coatings (ca. 50 MPa). This study demonstrates the potential of these surfaces to be applied onto a wide variety of material types, even polymeric materials, due to the lower processing temperatures utilised, with the vision to generate bioactive and/or antibacterial properties on a plethora of bioinert materials.

Outcome evaluation of new calcium titanate schanz-screws for external fixators. First clinical results and cadaver studies

OBJECTIVE

External fixators are important for correcting length discrepancies and axis deformities in pediatric or trauma orthopedic surgery. Pin loosening is a common pitfall during therapy that can lead to pain, infection, and necessary revisions. This study aims to present clinical data using calcium titanate (CaTiO₃) Schanz screws and to measure the fixation strength.

PATIENTS AND METHODS

22 titanate screws were used for external fixators in 4 pediatric patients. Therapy was initiated to lengthen or correct axial deformities after congenital abnormalities. The maximum tightening torque was measured during implantation, and the loosening torque was measured during explantation. In addition, screws of the same type were used in a cadaver study and compared with stainless steel and hydroxyapatite-coated screws. 12 screws of each type were inserted in four tibias, and the loosening and tightening torque was documented.

RESULTS

The fixation index in the in vivo measurement showed a significant increase between screw insertion and extraction in three of the four patients. The pins were in situ for 91 to 150 days, and the torque increased significantly (P = 0.0004) from insertion to extraction. The cadaveric study showed lower extraction torques than insertion torques, as expected in this setting. The calculated fixation index was significantly higher in the CaTiO₃ group than in the other groups (P = 0.0208 vs. HA and P < 0.0001 vs. steel) and in the HA group vs. plain steel group (P = 0.0448).

CONCLUSION

The calcium titanate screws showed favorable fixation strength compared to HA and stainless steel screws and should be considered in long-term therapy of external fixation.

Tri-Functional Calcium-Deficient Calcium Titanate Coating on Titanium Metal by Chemical and Heat Treatment

The main problem of orthopedic and dental titanium (Ti) implants has been poor bone-bonding to the metal. Various coatings to improve the bone-bonding, including the hydroxyapatite and titania, have been developed, and some of them have been to successfully applied clinical use. On the other hand, there are still challenges to provide antibacterial activity and promotion of bone growth on Ti. It was shown that a calcium-deficient calcium titanate coating on Ti and its alloys exhibits high bone-bonding owing to its apatite formation. In this study, Sr and Ag ions, known for their promotion of bone growth and antibacterial activity, were introduced into the calcium-deficient calcium titanate by a three-step aqueous solution treatment combined with heat. The treated metal formed apatite within 3 days in a simulated body fluid and exhibited antibacterial activity to Escherichia coli without showing any cytotoxicity in MC3T3-E1 preosteoblast cells. Furthermore, the metal slowly released 1.29 ppm of Sr ions. The Ti with calcium-deficient calcium titanate doped with Sr and Ag will be useful for orthopedic and dental implants, since it should bond to bone because of its apatite formation, promote bone growth due to Sr ion release, and prevent infection owing to its antibacterial activity.

Two Different Strategies to Enhance Osseointegration in Porous Titanium: Inorganic Thermo-Chemical Treatment Versus Organic Coating by Peptide Adsorption

In this study, highly-interconnected porous titanium implants were produced by powder sintering with different porous diameters and open interconnectivity. The actual foams were produced using high cost technologies: Chemical Vapor Deposition (CVD), Physical Vapor Deposition (PVD), and spark plasma sintering, and the porosity and/or interconnection was not optimized. The aim was to generate a bioactive surface on foams using two different strategies, based on inorganic thermo-chemical treatment and organic coating by peptide adsorption, to enhance osseointegration. Porosity was produced using NaCl as a space holder and polyethyleneglicol as a binder phase. Static and fatigue tests were performed in order to determine mechanical behaviors. Surface bioactivation was performed using a thermo-chemical treatment or by chemical adsorption with peptides. Osteoblast-like cells were cultured and cytotoxicity was measured. Bioactivated scaffolds and a control were implanted in the tibiae of rabbits. Histomorphometric evaluation was performed at 4 weeks after implantation. Interconnected porosity was 53% with an average diameter of 210 µm and an elastic modulus of around 1 GPa with good mechanical properties. The samples presented cell survival values close to 100% of viability. Newly formed bone was observed inside macropores, through interconnected porosity, and on the implant surface. Successful bone colonization of inner structure (40%) suggested good osteoconductive capability of the implant. Bioactivated foams showed better results than non-treated ones, suggesting both bioactivation strategies induce osteointegration capability.

A comparative study of simulated body fluids in the presence of proteins

Simulated body fluid (SBF) is widely used as part of an in vitro method to evaluate implant materials such as their apatite forming ability (AFA), a typical indication of potential bone-bonding ability in vivo. We report the use of carbonate-buffered SBFs as potential solutions for implant evaluation and the effect of proteins, represented by bovine serum albumin (BSA) in SBFs on the formation of hydroxyapatite (HA). These solutions are buffered by the thermodynamic equilibrium with 5% CO₂ in an incubator, and result in a deposition of carbonated HA. Using several titanium-based surfaces, these solutions were studied in comparison with the widely-used SBF (ISO 23317). The presence of BSA strongly inhibited the formation of HA in traditional SBF, while HA can still be observed in carbonate-buffered SBFs. A kinetic study reveals that the inhibitory effect is concentration dependent with 0.1g/L and 1g/L of BSA having little effect on HA growth but a complete inhibition of HA formation at 5g/L of BSA, as tested using NaOH treated titanium with a known positive AFA. The decrease in solution pH and free calcium concentrations in SBFs due to the addition of BSA is not significant, suggesting other causes for the strong inhibitory effect.

STATEMENT OF SIGNIFICANCE

The successful use of simulated body fluids (SBFs) to evaluate potential bioactive implants relies on the better understanding of the heterogeneous nucleation and growth of hydroxyapatite in solution. Although a standardized recipe for SBF was developed over a decade ago, a few key issues remain to be understood, i.e. the behavior of carbonate-buffered SBFs having similar buffering mechanism as human blood, and the effect of proteins on hydroxyapatite formation on bioactive materials. This paper addresses these two issues and would help the reader better understand the subtleties in this domain and better interpret the results generated using SBFs.

Bioactive macroporous titanium implants highly interconnected

Intervertebral implants should be designed with low load requirements, high friction coefficient and low elastic modulus in order to avoid the stress shielding effect on bone. Furthermore, the presence of a highly interconnected porous structure allows stimulating bone in-growth and enhancing implant-bone fixation. The aim of this study was to obtain bioactive porous titanium implants with highly interconnected pores with a total porosity of approximately 57 %. Porous Titanium implants were produced by powder sintering route using the space holder technique with a binder phase and were then evaluated in an in vivo study. The size of the interconnection diameter between the macropores was about 210 μm in order to guarantee bone in-growth through osteblastic cell penetration. Surface roughness and mechanical properties were analyzed. Stiffness was reduced as a result of the powder sintering technique which allowed the formation of a porous network. Compression and fatigue tests exhibited suitable properties in order to guarantee a proper compromise between mechanical properties and pore interconnectivity. Bioactivity treatment effect in novel sintered porous titanium materials was studied by thermo-chemical treatments and were compared with the same material that had undergone different bioactive treatments. Bioactive thermo-chemical treatment was confirmed by the presence of sodium titanates on the surface of the implants as well as inside the porous network. Raman spectroscopy results suggested that the identified titanate structures would enhance in vivo apatite formation by promoting ion exchange for the apatite formation process. In vivo results demonstrated that the bioactive titanium achieved over 75 % tissue colonization compared to the 40 % value for the untreated titanium.

Biomineralization of Engineered Spider Silk Protein-Based Composite Materials for Bone Tissue Engineering

Materials based on biodegradable polyesters, such as poly(butylene terephthalate) (PBT) or poly(butylene terephthalate-co-poly(alkylene glycol) terephthalate) (PBTAT), have potential application as pro-regenerative scaffolds for bone tissue engineering. Herein, the preparation of films composed of PBT or PBTAT and an engineered spider silk protein, (eADF4(C16)), that displays multiple carboxylic acid moieties capable of binding calcium ions and facilitating their biomineralization with calcium carbonate or calcium phosphate is reported. Human mesenchymal stem cells cultured on films mineralized with calcium phosphate show enhanced levels of alkaline phosphatase activity suggesting that such composites have potential use for bone tissue engineering.

Characterization of Ti6Al7Nb alloy foams surface treated in aqueous NaOH and CaCl2 solutions

Ti6Al7Nb alloy foams having 53-73% porosity were manufactured via evaporation of magnesium space holders. A bioactive 1µm thick sodium hydrogel titanate layer, NaxH2-xTiyO2y+1, formed after 5M NaOH treatment, was converted to crystalline sodium titanate, Na2TiyO2y+1, as a result of post-heat treatment. On the other hand, subsequent CaCl2 treatment of NaOH treated specimens induced calcium titanate formation. However, heat treatment of NaOH-CaCl2 treated specimens led to the loss of calcium and disappearance of the titanate phase. All of the aforementioned surface treatments reduced yield strengths due to the oxidation of the cell walls of the foams, while elastic moduli remained mostly unchanged. Accordingly, equiaxed dimples seen on the fracture surfaces of as-manufactured foams turned into relatively flat and featureless fracture surfaces after surface treatments. On the other hand, Ca- and Na-rich coating preserved their mechanical stabilities and did not spall during fracture. The relation between mechanical properties of foams and macro-porosity fraction were found to obey a power law. The foams with 63 and 73% porosity met the desired biocompatibility requirements with fully open pore structures and elastic moduli similar to that of bone. In vitro tests conducted in simulated body fluid (SBF) showed that NaOH-heat treated surfaces exhibit the highest bioactivity and allow the formation of Ca-P rich phases having Ca/P ratio of 1.3 to form within 5 days. Although Ca-P rich phases formed only after 15 days on NaOH-CaCl2 treated specimens, the Ca/P ratio was closer to that of apatite found in bone.

Hydrothermal treatment of Ti surface to enhance the formation of low crystalline hydroxyl carbonate apatite

Background

Ti and its alloys have been widely used as orthopedic and dental implants due to their outstanding mechanical properties and biocompatibility. However, long time is required to form bond between Ti implant and surrounding tissues. Therefore, these implants necessitate surface treatment such as mechanical/chemical treatment and coating of bioactive materials for improving the osseointegration.

Results

This study was focused on the calcium-phosphate (Ca-P) coating on machined Ti, blasted-Ti (B-Ti), and blasted-NaOH-etched-Ti (BNH) surfaces by hydrothermal method to evaluate the ability of HA formation. Nanostructured morphology was created by NaOH etching on blasted-Ti surface. XRD analysis confirmed the existence of sodium titanate phase on such samples. Rutile and anatase phases along with hydroxyapatite were observed after hydrothermal treatment in Ca-P solution. Substantial hydroxyapatite together with TiO₂ was observed during hydrothermal treatment at 200°C for 12 hrs. Blasted-NaOH-etched samples (BNH-Ti) revealed appreciable bone-like apatite formation as compared to machined-Ti and blasted-Ti (B-Ti) surfaces. However, maximum HA formation was confirmed on Ca-P coated-BNH samples (BNHA-Ti-200-12) by XRD and ICP analysis.

Conclusion

Multistep surface treatment adopted in current study would be effective to enhance HA formation on Ti surface.